I use BoreTech and it works great. If you are strapped for cash don't worry about it, you made an effort.
Everytime I've bought a used gun I figure it's my responsibility to get it clean to my satisfaction, not the seller's.
Would you be upset if you bought a used gun online and the barrel had some copper fouling in it? I feel like I would be.
Nope. Rifles NIB from the factory have copper streaks from test firing at the factory.